I've destroyed 3 acrylic idler wheels in the past 2 months.  If you have a MakerBot, you've probably broken one too... or will break one soon.  Maybe I was just really unlucky.  I did get an almost double sized 4.5mm acrylic wheel from MakerGear and it has held up well and may never break, but I always felt like it was only a matter of time.

Brian Reifsnyder makes and sells RepRap barrels in his shop and offered to make me an aluminum wheel design he's been working on.  He's cutting a groove in the side to help grab ahold of the filament more tightly.  I'm not entirely sure how effective the groove is or if it's preventing an even tighter grip, however I did noticed that the filament doesn't sway back and forth at the top as it feeds in like it used to.  So that groove seems to hold it in place better and feed it straighter down into the barrel.  We tried one that was 4mm thick, but with the groove it wasn't able to get close enough with the bottom lip of the motor pulley getting in the way.  Then we tried a 3mm thick wheel and that seems to be perfect.  I had to put 1 full sized washer and 1 half sized washer (that I had gotten from MakerGear with his 4.5mm wheel) under it, and 1 full sized washer on top of it to get the height just right.  Also, I've removed the top flange from the motor pulley.  It fell off a while back during one of the many rebuilds.  Doesn't seem to be needed and gives you a little more space for the idler wheel.

Hopefully I'll never have to worry about a cracked idler wheel ever again!  If you're interested in getting one yourself, email Brian for more information.

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